Adsorbents carbon fibers

Detailed accounts of fibers and carbon-carbon composites can be found in several recently published books [1-5]. Here, details of novel carbon fibers and their composites are reported. The manufacture and applications of adsorbent carbon fibers are discussed in Chapter 3. Active carbon fibers are an attractive adsorbent because their small diameters (typically 6-20 pm) offer a kinetic advantage over granular activated carbons whose dimensions are typically 1-5 mm. Moreover, active carbon fibers contain a large volume of mesopores and micropores. Current and emerging applications of active carbon fibers are discussed. The manufacture, structure and properties of high performance fibers are reviewed in Chapter 4, whereas the manufacture and properties of vapor grown fibers and their composites are reported in Chapter 5. Low density (porous) carbon fiber composites have novel properties that make them uniquely suited for certain applications. The properties and applications of novel low density composites developed at Oak Ridge National Laboratory are reported in Chapter 6. 

Economy, J., Foster, K., Andreopoulos, A. and Jung, H., Tailoring carbon fibers for adsorbing volatiles, CHEMTECH, October 1992, 597 603. 

Anisimov, V. N., Zabezhinski, M. A., Popovich, I. G., Liebcrman, A. I. and Shmidt, J. L., Prevention of spontaneous and chemically-induecd earcinogenesis using activated earbon fiber adsorbent. I. Effeet of the aetivated carbon fiber adsorbent Aqualen on spontaneous carcinogenesis and life span in mice. Cancer Lett., 1998, 126(1), 23 28. 

A recently developed adsorbent version of ORNL s porous carbon fiber-carbon binder eomposite is named carbon fiber composite molecular sieve (CFCMS). The CFCMS monoliths were the product of a collaborative researeh program between ORNL and the University of Kentueky, Center for Applied Energy Researeh (UKCAER) [19-21]. The m.onoliths are manufactured in the manner deseribed in Section 2 from P200 isotropic pitch derived fibers. While development of these materials is in its early stages, a number of potential applieations can be identified. 

Burchell, T.D., Judkins, R.R. and Rogers, M.R., A carbon fiber based monolithic adsorbent for gas separation. In Proc. 23rd Biennial Con/, on Carbon, American Carbon Society, 1997, pp. 158 159. 

In addition to the particulate adsorbents listed in Table 16-5, some adsorbents are available in structured form for specific applications. Monoliths, papers, and paint formulations have been developed for zeolites, with these driven by the development of wheels (Fig. 16-60), adsorptive refrigeration, etc. Carbon monoliths are also available as are activated carbon fibers, created from polymeric materials, and sold in the forms of fabrics, mats, felts, and papers for use in various applications including in pleated form in filters. Zeolitic and carbon membranes are also available, with the latter developed for separation by selective surface flow [Rao and Sircar, J. Membrane Sci., 85, 253 (1993)]. 

As alternative materials to traditional particulate active carbons, much research has been carried out on the potential of active carbon fibers as gas and liquid phase adsorbents and catalysts/catalyst supports, as outlined below. 

The major potential application of active carbon fibers is as an adsorbent in environmental control, as outlined in the previous section. However, there is a number of smaller scale, niche applications that seem to be particularly suited to ACF. These emerging applications include the use of ACF in medicine [111 (see also 59,60),112], as capacitors [113-119] and vapor sensors [120], and in refrigeration [121]. The first two of these applications are summarized below. However, there are not many detailed, publicly-available sources describing any of these applications, partly for commercial reasons and partly because the technology is emerging, so any summary is necessarily limited in scope. 

The SFg molecules adsorb in this type of carbon system if the carbon fiber/cloth is oxidized at 400-450°C under mild oxidation conditions. 

Graphite and carbon fibers have been used at templates. Thus, nylon 6 has been polymerized on a graphite matrix. Such syntheses of polymers in the presence of a solid template, where the solid acts as a template have been described as polymerization-induced epitaxy (PIE). The monomer and resulting film is adsorbed on the template surface through only van der Waals forces. After polymerization, the polymer is washed from the template. The recovered polymer retains special structural features introduced by the template. 

We have an excellent activated carbon of fiber morphology, so called activated carbon fiber ACF[3]. This ACF has considerably uniform slit-shaped micropores without mesopores, showing characteristic adsorption properties. The pore size distribution of ACF is very narrow compared with that of traditional granular activated carbon. Then, ACF has an aspect similar to the regular mesoporous silica in particular in carbon science. Consequently, we can understand more an unresolved problem such as adsorption of supercritical gas using ACF as an microporous adsorbent. 

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